The present invention relates to a novel organic-inorganic composite graded material, a process for the production thereof and its use. More specifically, the present invention relates to an organic-inorganic composite graded material comprising a chemical bond product in which an organic polymer compound and a metallic compound are chemically bonded to each other, having a component-graded structure in which the content of the metallic compound continuously varies along the thickness direction of the material and being useful as a functional material in various fields, a process for efficiently producing the above material, a coating agent made of the above graded material for forming a coating, such as a coating film, an adhesive for bonding an organic material to an inorganic or metallic material or an intermediate film to be interposed between an organic substrate and an inorganic or metallic material layer, and base materials or articles for which the above graded material is applied.
In recent years, with a diversification of demands to performances and functions of organic polymer materials, it is difficult to comply with such demands with a single polymer compound, and a different material having different properties is added to a polymer compound to form a composite compound.
For example, it is general practice to disperse a reinforcing material in an organic polymer material to modify the physical properties of the polymer material. Specifically, an organic or inorganic fibrous material such as a carbon fiber, a glass fiber, a metal fiber, a ceramic fiber, an aramid fiber, etc., or a powdery inorganic filler of calcium carbonate, silica, alumina, etc., is added and homogeneously dispersed.
Further, studies are actively made by mixing different polymer compounds, optionally, together with a compatibilizer to form a polymer alloy which exhibits novel functions.
A graded functional material recently attracts attention, which material is a composite material obtained by gradually changing the composition of the material so that the properties of its front and reverse completely differ from each other. For example, a metal-ceramic composite graded functional material having both the heat resistance of ceramic and the strength of metal has been developed as an airframe material of a supersonic aircraft.
Such graded functional materials are classified into an inorganic graded material, an organic graded material and an organic-inorganic composite graded material. These graded functional materials are prepared by mixing a plurality of materials such as a plurality of inorganic materials of different kinds, a plurality of organic materials of different kinds or a combination of at least one organic material and at least one inorganic material and controlling these materials such that their distribution density, orientation, etc., differ from place to place. The graded functional materials can exhibit properties of a plurality of component materials. It is therefore expected that the above materials can be applied to the filed of aerospace industries, the field of automobiles, the field of electronics, the medical field, the field of energy and, further, the filed of shields against radiations and electromagnetic waves.
Meanwhile, since there was found a so-called Honda-Fujishima effect that water is photodecomposed into hydrogen and oxygen when a semiconductor such as titanium dioxide is used as a photoelectrode (xe2x80x9cKogyo Kagaku Zasshixe2x80x9d, Vol. 72, pages 108 to 113 (1969)), studies have been vigorously made to develop photocatalysts and put them into practical use. For example, when semiconductor particles of titanium dioxide are excited with light having energy greater than their band gap, electrons are generated in a conduction band, and holes are generated in a valence band. The above photocatalysts utilize electron-hole pairs rich with energy.
Application of the above photocatalysts has been and is studied not only for deodorization, anti-fouling, an anti-microbial function and disinfection but also for decomposition and removal of various environmentally detrimental substances in drain or waste gas.
As photocatalysts, various compounds having semiconductive property are known. For example, there are known metal oxides such as titanium dioxide, iron oxide, tungsten oxide and zinc oxide and metal sulfides such as cadmium sulfide and zinc sulfide. Of these, titanium dioxide, particularly anatase type titanium dioxide, is useful as a practical photocatalyst. This titanium dioxide exhibits excellent photocatalysis when it absorbs light having a specific wavelength in an ultraviolet region included in usual light such as sunlight. Due to strong oxidation activity derived from the above photocatalysis, the titanium dioxide exhibits functions such as anti-fouling, deodorization, anti-microbial function, air-cleaning, water-cleaning and super-hydrophilicity.
Studies are being actively made at present to allow the photocatalyst such as titanium dioxide or the like to exhibit the above photocatalytic functions for their industrial utility. For example, when the photocatalyst is coated on a material surface or incorporated into a coating on a material surface in advance, it is possible to impart the material surface with the function of a decomposer of an organic substance only upon irradiation with light, and its practical use has begun for glass and tiles that are not easily soiled or a stool. Further, studies are being actively made for developing various functional articles utilizing the above photocatalyst. For example, studies are being made with regard to practical use of (1) construction materials capable of decomposing nitrogen oxide that constitutes a source of air pollution, with light energy of the sun, (2) glass having a surface coating made of a transparent photocatalyst, having capability of naturally decomposing an adhering soiling and having an anti-microbial effect, (3) a window film having a photocatalyst layer formed on its surface for utilizing the ultra-hydrophilic nature and an anti-fouling performance of the photocatalyst and being to be applied to a front surface side of a glass window and (4) a drain treating agent formed by coating silica gel particles with a fine titanium dioxide powder.
The photocatalysts having photocatalytic function such as titanium dioxide cannot be easily supported on an organic substrate such as a plastic substrate, and most of them require some binder. Further, when the photocatalyst is coated directly on an organic substrate or incorporated into such a substrate, there is caused a problem that the organic substrate inevitably deteriorates for a short period of time due to the photocatalysis.
For overcoming the above problem, attempts are made to form a coating film made of a photocatalyst such as titanium dioxide on the organic substrate through an organic adhesive. In this case, however, there is incurred an undesirable situation in which the adhesion between the binder and the photocatalyst decreases with the passage of time or opacification, an interference color, etc., are caused. Attempts are also made to form a coating film made of a photocatalyst such as titanium dioxide on the organic substrate through an inorganic adhesive. In this case, the adhesion to the substrate is not sufficient or the adhesive layer itself undergoes cracking, resulting in an undesirable situation in which the adhesion between the binder and the substrate decreases with the passage of time or opacification, an interference color, etc., are caused. Further, microcapsules formed by coating a photocatalyst such as titanium dioxide with silica have been developed, and attempts are made to incorporate the microcapsules into an organic substrate for imparting the organic substrate with deodorization and anti-microbial functions. In the above microcapsules, the photocatalyst is not easily exposed on a surface, so that the deterioration of the organic substrate is inhibited. Further, each capsule has a number of fine pores, and organic substances having small molecules can enter them, so that the catalytic function is effectively exhibited. However, the microcapsules having such a structure are difficult to improve in photocatalytic activity, and it is also difficult to fully apply the phenomenon of conversion to hydrophilic nature that is another characteristic feature of the photocatalyst. Further, the microcapsules had a defect that the production process thereof requires complicated procedures so that the production cost thereof is inevitably large.
On the other hand, it is general practice to form layers made of various inorganic or organic materials other than the above materials for photocatalytic activity, such as a conductive material, a hard coating agent, an optical recording material, a magnetic powder, an infrared-absorbing material, etc., on a plastic substrate to produce functional materials.
When the above inorganic or metallic material layer is formed on a plastic substrate, for example, there is often employed a method in which an inorganic primer layer is formed on the plastic substrate and the inorganic or metallic material layer is formed thereon, since the adhesion thereof to the substrate is generally insufficient. In this method, the adhesion between the inorganic primer layer and the inorganic or metallic material layer is good. However, the adhesion between the plastic substrate and the inorganic primer layer is not always sufficient, and there is involved a problem that the durability of the adhesion against heat is poor or that the adhesion decreases with the passage of time.
It has been therefore desired to develop a technique of forming an inorganic or metallic material layer on a plastic substrate with good adhesion.
Under the circumstances, it is an object of the present invention to provide an organic-inorganic composite graded material having a composition continuously changing in its thickness direction, which is useful as a novel functional material in various fields, such as a coating, an adhesive between an organic material and an inorganic or metallic material, an intermediate film which is formed between an organic substrate and a coating made of a photocatalyst and prevents deterioration of the organic substrate or an intermediate film for improving the adhesion between an organic substrate and an inorganic or metallic material, a process for efficiently producing the above material and a use thereof.
For achieving the above object, the present inventors have made diligent studies and as a result have found that an organic-inorganic composite material in which an organic polymer compound and a metallic compound are chemically bonded to each other, obtained by applying a coating solution, which is a mixture of an organic polymer compound having a metal-containing group capable of bonding to a metal oxide or metal nitride polymer compound by hydrolysis in a molecule with a metal compound capable of forming a metal oxide by hydrolysis or a metal nitride polymer compound, or a hydrolysis product of the above mixture, on an organic substrate and drying a formed coating under heat, is a novel organic-inorganic composite graded material having a component-graded structure in which the content of the metallic compound in the material continuously changes in the depth direction from the material surface, and is useful for the above use. The present invention has been accordingly completed on the basis of the above finding.
That is, the present invention provides:
(1) an organic-inorganic composite graded material in which an organic polymer compound and a metallic compound are chemically bonded to each other, and having a component-graded structure in which the content of the metallic compound in the material continuously changes in the depth direction from the surface of the material,
(2) a coating agent made of the above organic-inorganic composite graded material for forming a film on a substrate, preferably, a coating agent for forming a coating film on an organic substrate, as an adhesive for bonding an organic material to an inorganic or metallic material and for forming an intermediate film to be interposed between an organic substrate and a coating layer containing at least an inorganic or metallic material,
(3) a substrate using the above organic-inorganic composite graded material,
(4) an organic-inorganic bonding material using the above organic-inorganic composite graded material as an adhesive, and
(5) an article having the above organic-inorganic composite graded material interposed as an intermediate film and having a coating layer containing at least an inorganic or metallic material.
According to the present invention, further, the above organic-inorganic composite graded material can be produced by preparing a coating solution which is a mixture of (A) an organic polymer compound having a molecule containing a metal-containing group capable of bonding to a metal oxide or metal nitride polymer by hydrolysis with (B) (a) a metal compound capable of forming a metal oxide by hydrolysis or (b) a metal nitride polymer or preparing a hydrolysis product of the mixture, forming a coating film made of the above coating solution on a substrate made of an organic material and drying the coating film under heat.